Navigating the locations (by mouse, or W, A, S, D keys) in the game brings hotspots into range, shown either with a magnifying glass or a hand. The former indicates something you can look at, the latter something with which you can interact. An interaction may require a specific inventory item to be highlighted in Watson's medical bag (which forms your inventory). You can access the inventory with the 'I' key, or by right clicking.

The game can be played with mouse OR keyboard, or a combination of the two, as suits your style. As a fairly regular Dark-sider, I find keyboard controls easy, and the mouse was a bit slower, but I can't recall anything in the game that's impossible with just the mouse.